1. Field of the Invention
The present invention relates to a relay finder optical system of a single-lens reflex (SLR) camera.
2. Description of the Prior Art
A finder optical system of an SLR camera has a fundamental structure in which an image formed on a primary imaging plane (focusing plate) through a photographing lens system is re-formed on a secondary imaging plane through a relay finder optical system, and the secondary image is viewed by the photographer through a Lupe (magnifying) optical system (an eyepiece optical system). For example, Japanese Unexamined Patent Publication Nos. 2001-290087 and 2003-121760 can be taken as the prior art.
If an attempt is made to reduce the magnification of the relay finder optical system, the size of the secondary imaging plane can be made smaller with respect to the size of the field-of-view frame. Consequently, such a smaller magnification of the relay finder optical system contributes to further miniaturization of the camera (finder optical system).
On the other hand, in order to increase the magnification of the finder optical system, the focal length of the Lupe (magnifying) optical system is inevitably made shorter; and as a result, the eye relief becomes shorter, the diameter of the Lupe (magnifying) optical system becomes larger, and the structure of the Lupe (magnifying) optical system is complicated.
Conversely, if an attempt is made to enlarge the magnification of the relay finder optical system, not only the relay finder optical system but also the Lupe (magnifying) optical system is inevitably enlarged, so that the finder optical system (camera) cannot be miniaturized.